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Chapter 8. Using Fibre Channel devices
Red Hat Enterprise Linux 9 provides the following native Fibre Channel drivers:
-
lpfc
-
qla2xxx
-
zfcp
8.1. Resizing Fibre Channel logical units
As a system administrator, you can resize Fibre Channel logical units.
Procedure
Determine which devices are paths for a
multipath
logical unit:# multipath -ll
Re-scan Fibre Channel logical units on a system that uses multipathing:
$ echo 1 > /sys/block/sdX/device/rescan
Additional resources
-
multipath(8)
man page on your system
8.2. Determining the link loss behavior of device using Fibre Channel
If a driver implements the Transport dev_loss_tmo
callback, access attempts to a device through a link will be blocked when a transport problem is detected.
Procedure
Determine the state of a remote port:
$ cat /sys/class/fc_remote_ports/rport-host:bus:remote-port/port_state
This command returns one of the following output:
-
Blocked
when the remote port along with devices accessed through it are blocked. Online
if the remote port is operating normallyIf the problem is not resolved within
dev_loss_tmo
seconds, therport
and devices will be unblocked. All I/O running on that device along with any new I/O sent to that device will fail.
-
When a link loss exceeds dev_loss_tmo
, the scsi_device
and sd_N_
devices are removed. Typically, the Fibre Channel class will leave the device as is, that is /dev/sdx
will remain /dev/sdx
. This is because the target binding is saved by the Fibre Channel driver and when the target port returns, the SCSI addresses are recreated faithfully. However, this cannot be guaranteed, the sdx
device will be restored only if no additional change on in-storage box configuration of LUNs is made.
Additional resources
-
multipath.conf(5)
man page on your system - Recommended tuning at scsi,multipath and at application layer while configuring Oracle RAC cluster (Red Hat Knowledgebase)
8.3. Fibre Channel configuration files
The following is the list of configuration files in the /sys/class/
directory that provide the user-space API to Fibre Channel.
The items use the following variables:
H
- Host number
B
- Bus number
T
- Target
L
- Logical unit (LUNs)
R
- Remote port number
Consult your hardware vendor before changing any of the values described in this section, if your system is using multipath software.
Transport configuration in /sys/class/fc_transport/targetH:B:T/
port_id
- 24-bit port ID/address
node_name
- 64-bit node name
port_name
- 64-bit port name
Remote port configuration in /sys/class/fc_remote_ports/rport-H:B-R/
-
port_id
-
node_name
-
port_name
dev_loss_tmo
Controls when the scsi device gets removed from the system. After
dev_loss_tmo
triggers, the scsi device is removed. In themultipath.conf
file , you can setdev_loss_tmo
toinfinity
.In Red Hat Enterprise Linux 9, if you do not set the
fast_io_fail_tmo
option,dev_loss_tmo
is capped to600
seconds. By default,fast_io_fail_tmo
is set to5
seconds in Red Hat Enterprise Linux 9 if themultipathd
service is running; otherwise, it is set tooff
.fast_io_fail_tmo
Specifies the number of seconds to wait before it marks a link as "bad". Once a link is marked bad, existing running I/O or any new I/O on its corresponding path fails.
If I/O is in a blocked queue, it will not be failed until
dev_loss_tmo
expires and the queue is unblocked.If
fast_io_fail_tmo
is set to any value except off,dev_loss_tmo
is uncapped. Iffast_io_fail_tmo
is set to off, no I/O fails until the device is removed from the system. Iffast_io_fail_tmo
is set to a number, I/O fails immediately when thefast_io_fail_tmo
timeout triggers.
Host configuration in /sys/class/fc_host/hostH/
-
port_id
-
node_name
-
port_name
issue_lip
Instructs the driver to rediscover remote ports.
8.4. DM Multipath overrides of the device timeout
The recovery_tmo
sysfs
option controls the timeout for a particular iSCSI device. The following options globally override the recovery_tmo
values:
-
The
replacement_timeout
configuration option globally overrides therecovery_tmo
value for all iSCSI devices. For all iSCSI devices that are managed by DM Multipath, the
fast_io_fail_tmo
option in DM Multipath globally overrides therecovery_tmo
value.The
fast_io_fail_tmo
option in DM Multipath also overrides thefast_io_fail_tmo
option in Fibre Channel devices.
The DM Multipath fast_io_fail_tmo
option takes precedence over replacement_timeout
. Red Hat does not recommend using replacement_timeout
to override recovery_tmo
in devices managed by DM Multipath because DM Multipath always resets recovery_tmo
, when the multipathd
service reloads.